1. Field of the Invention
The present invention relates to an image processing method, image processing apparatus, control method thereof and, more particularly, to an image processing method for receiving and printing image data, an image processing apparatus having the function of the method, and a control method thereof.
2. Description of the Related Art
As printer technologies have advanced, the resolution of output onto media such as paper sheets is increasing. As the printer resolution increases, there are merits of improving the smoothness of lines and the tonality of colors represented by pseudo halftone. However, processing for generating a digital image (so-called rendering processing) requires a longer processing time and a larger memory size with increasing resolution, and the image quality and processing cost have a trade-off relationship.
As a conventional technique for speeding up high-resolution rendering processing, Japanese Patent Laid-Open Nos. 2000-137825 and 2000-149035 disclose a technique for efficiently sorting intersections of borders of objects.
Also, Japanese Patent Laid-Open No. 10-202960 discloses a technique for reducing the cost of rendering processing by rendering only a specific portion in a page to have a high resolution.
Furthermore, as a generally known technique, a smoothing technique which increases an output resolution by applying pixel interpolation and edge-shape pattern matching to a low-resolution, rendered image is popularly used.
However, even using the technique disclosed in Japanese Patent Laid-Open Nos. 2000-137825 and 2000-149035, high-resolution rendering often cannot sufficiently shorten the processing time or reduce the consumed memory size. In this case, it is effective to partially use low-resolution rendering within a range that does not influence image quality.
As a method of effectively improving print image quality while suppressing processing cost, high-resolution rendering processing may be executed while restricting it to only small characters and thin lines. However, it is impossible for the smoothing technique to improve the proportion of small characters of several points or less, or to express a high-resolution one-dot line.
On the other hand, with the technique disclosed in Japanese Patent Laid-Open No. 10-202960, since the resolution is decided for each area, a drawing object other than small characters and thin lines in a high-resolution area is also rendered to have a high resolution. For this reason, apparent unnaturalness due to changes in dot width and image quality occurs at the boundary with a neighboring low-resolution area.